Spectroscopic investigation of zwitterion formation in hydrated amino acid clusters Mark A. Johnson, Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520 Mapping backbone deformations upon complexation: The vibrational fingerprint regions of the X-H+-Y binary complexes yield insight into the structural deformations suffered by the X and Y subunits upon binding to a common proton. Comparing the known infrared spectra of the neutral X and Y species (A and B) to those of the protonated monomers (C and D), we can quantify the degree to which each moiety is effectively protonated in the dimer. A B C D G E F